1. Field of the Invention
The present invention relates to a magnetic field measurement apparatus consisting of a magnetometer comprised of a Superconductive Quantum Interferometer Device (SQUID) for measuring magnetic fields generated by the nervous activity of the brain of humans or animals or myocardial activity or magnetic substances contained in the subject to be inspected.
2. Description of Related Art
In measurements of very weak magnetic fields in the conventional art using equipment such as SQUID for measuring biomagnetic fields, generally the magnetic field on the surface of a living body is capable of being measured. Such measurements can be just the vertical components of a magnetic field with the head regarded as a sphere, for instance the polar coordinates (r, ø, θ) in the case of the head, and the magnetic field component Br in the vertical r direction on the head surface, or in the case of the heart, the orthogonal coordinates (X, Y, Z), of the chest section when measured on the flat planes X and Y, and the magnetic field component BZ. in the vertical Z direction on the X and Y planes.
On the other hand while few in number, there is literature reporting on measurement apparatus for measuring magnetic components of a biomagnetic field in a plurality of directions. For instance, the simultaneous measurement of the magnetic component BX in the X direction and the magnetic component BY in the Y direction on the orthogonal coordinates (X, Y, Z); as well as the display of magnitude √(BX2+BY2) synthesized by magnetic component BX in the X direction and magnetic component BY in the Y direction have been reported (K. Tsukada et. al., Rev. Sci. Instrum., 66 (10), pp 5085-5091(1995)).
Further, though not the three directions Br, Bø, Bθ of the polar coordinates (r, ø, θ) of the magnetic components BX, BY and BZ in the three directions of the orthogonal coordinates (X, Y, Z); a method has been reported for measuring the three components of each intersecting magnetic field, finding the magnetic components Br, Bø, Bθ in the three directions on the polar coordinates (r, ø, θ) and displaying a waveform showing the time variation of each magnetic component in three directions on polar coordinates (r, ø, θ) on a CRT screen (Y. Yoshida et. al., 10th Int'l Conf. on Biomagnetisim (1996)).
Also, in the conventional art, not only a waveform showing time variations in a magnetic field strength but also the distribution of the magnitude of a magnetic field can be found from results of magnetic measurements of a plurality of points in an organism utilizing a plurality of magnetometers and the result displayed as a magnetic field magnitude contour map. Factors such as the position, magnitude and direction of electrical current sources in an organism can be analyzed over desired periods of time on a magnetic field contour map and changes over time in the electrical physiological phenomenon in the organism thus discovered. In the conventional art, changes in electrical physiological phenomenon in a dynamic organism can therefore be revealed by utilizing these magnetic field contour maps to aid in the diagnosis of disease.
In the method used in the conventional art, the heart of the child or adult which is the subject of measurement is fixed in a constant position and direction versus the magnetic plane of the magnetic field of the magnetometer. However, there is the problem that when measuring the magnetic field of the heart of a fetus, an accurate measurement of the heart's magnetic field cannot be made since the position and direction of the fetus cannot be fixed since the fetus is constantly moving within the body of the mother. In other words, even if there is no change in the electrical current source within the heart of the fetus the position and direction will change versus the magnetic plane of the magnetic field generated in the magnetometer by the heart of the fetus creating the problem that the time waveform and the components of the magnetic field being measured cannot be fixed. Another problem in the conventional art, is that a standardized waveform cannot be obtained due to variations in the magnetic field waveform due to changes in the body position of the fetus within the body of the mother, making an accurate diagnosis of the heart disease of the fetus difficult. Further, when the position of the Dewar's vessel housing the magnetometer is moved in order to increase the magnetic signal to measure the component in just one direction of the magnetic field, the magnetic signal reaches a maximum and the measurement range narrows so that setting an ideal position and direction for measurement with the Dewar's vessel is difficult creating the problem that a long time is required. A still further problem is that a large drift occurs in the magnetic signal being detected when moving the Dewar's vessel to an optimal position versus the subject being measured and a long time is thus required to stabilize the magnetic signal being detected.
Yet another problem is that high sensitivity non-destructive inspection of minute impurities having magnetic properties within a nonmagnetic substance is difficult and furthermore the investigation cannot be conducted with high speed.